Synthesis and Characterization of Mixed Chalcogen Triangular Complexes with New Mo₃(μ₃-S)(μ₂-Se₂)₃⁴⁺ and M₃(μ₃-S)(μ₂-Se)₃⁴⁺(M = Mo, W) Cluster Cores

In our pursuit of mixed chalcogen-bridged cluster complexes, solids of the compositions Mo3SSe6Br4 and W3SSe6Br4 were prepared using high-temperature synthesis from the elements. Treatment of Mo3SSe6Br4 with Bu4NBr in a vibration mill yielded (Bu4N)3{[Mo3(μ3-S)(μ2-Se2)3Br6]Br} (I). Its all-selenide analogue (Bu4N)3{[Mo3(μ3-Se)(μ2-Se2)3Br6]Br} (II) was prepared from Mo3Se7Br4 in a similar way. Both compounds were characterized by IR, Raman, and 77Se NMR spectroscopy. The structure of II was determined by X-ray single-crystal analysis. Compound I is isostructural with II and contains the new Mo3(μ3-S)Se64+ cluster core. By treatment of a 4 M Hpts solution of I with PPh3 followed by cation-exchange chromatography, the new mixed chalcogenido-molybdenum aqua ion, [Mo3(μ3-S)(μ2-Se)3(H2O)9]4+, was isolated and characterized using UV−vis spectroscopy and, after derivatization into [Mo3(μ3-S)(μ2-Se)3(acac)3(py)3]+, electrospray ionization mass spectrometry. From HCl solutions of the aqua ion, a supramolecular adduct with cucurbit[6]uril (CB[6]), {[Mo3(μ3-S)(μ2-Se)3(H2O)6Cl3]2CB[6]}Cl2·11H2O (III), was isolated and its structure determined using X-ray crystallography. W3SSe6Br4 upon reaction with H3PO2 gave a mixture of all of the [W3SxSe4−x(H2O)9]4+ species. After repeated chromatography, crystals of {[W3(μ3-S)(μ2-Se)3(H2O)7Cl2]2CB[6]}Cl4·12H2O (IV) were crystallized from the fraction rich in [W3(μ3-S)Se3(H2O)9]4+ and structurally characterized.